In a large bowl, combine 2 Tbs. of the olive oil, 2 tsp. of the parsley, the chives, red pepper flakes, cayenne, and salt. Add the shrimp and stir to coat evenly. Cover the bowl with plastic and marinate in the refrigerator for about 20 minutes.
Bring a large pot of well-salted water to a boil over high heat.
In a small sauté pan, heat 2 Tbs. of the olive oil over medium heat. Add the breadcrumbs and cook, stirring frequently, until lightly browned, 1 to 3 minutes. Transfer to a small bowl and let cool. Mix the remaining 1 Tbs. parsley, the mint, a grinding of pepper, and a pinch of salt into the breadcrumbs.
Heat the remaining 1/3 cup olive oil in a 12-inch skillet over medium heat. When the oil is hot, add the shallots and cook, stirring occasionally, until lightly browned, 2 to 4 minutes.
Put the spaghetti in the boiling water and cook until just shy of al dente, about 5 minutes.
While the spaghetti cooks, add the shrimp and halved tomatoes to the skillet. Season with salt and pepper and cook, stirring frequently, until the tomatoes start to soften and the shrimp is nearly cooked through, about 5 minutes.
Reserve 1/2 cup of the pasta-cooking water and drain the spaghetti. Return the pasta and 2 Tbs. of the reserved water to the pot. Add the shrimp mixture and toss over medium heat until the shrimp is cooked through and the spaghetti is perfectly al dente, 1 to 2 minutes more. Add more of the pasta water as necessary to keep the dish moist. Season to taste with salt and pepper, transfer to warm shallow bowls, and top each serving with the breadcrumbs.